As a three-way catalyst which can simultaneously clean up carbon monoxides (CO), hydrocarbons (HC) and nitrogen oxides (NOx) contained in an exhaust gas, noble metals such as Pt (platinum), Rh (rhodium) and Pd (palladium) have widely been used as a catalytically active component.
For example, there is proposed an exhaust gas purifying catalyst in which after an yttria (Y)-zirconia (Zr) composite oxide is obtained, an aqueous dinitrodiammine platinum solution is added to the composite oxide and then evaporated to dryness to support platinum (Pt) on the composite oxide (see, for example, following Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Publication No. 2000-262898)